Heavy metals in intact and resuspended sediments of a California reservoir, with emphasis on potential bioavailability of copper and zinc

Abstract

Alternatives to a bulk sediment metals approach were used to characterize the potential bioavailability of sediment zinc, copper, and cadmium in a California reservoir affected by historic mining wastes. Acid volatile sulfide (AVS) concentrations in the sediment were compared, on a molar basis, to metals that were extracted simultaneously with AVS. Acid volatile sulfide binding accounted for approximately 24% of the acid-soluble Zn, Cu, and Cd from shallow sediments and 81% from the deeper, depositional sediments. Metal sulfide solubility relations predicted the dissolved zinc: copper ratio that was found in interstitial water. The behaviour of sediment metals upon resuspension into overlying water was also investigated, using a calibrated, portable resuspension device on intact sediment cores. Total metals concentrations in overlying water demonstrated a significant positive, exponential relationship with resuspension energy. In time-series settling experiments, total metals concentrations declined exponentially in hours to days as particles fell out of solution. The most notable finding was that dissolved metals (0.45 �m filtration) did not increase significantly above background water column concentrations at any resuspension energy and remained low throughout time series up to 120 h. This suggests the presence of alternate metals-binding capacity in the sediments in addition to AVS. Zinc exhibited lower dissolved concentrations in overlying water with increasing resuspension.